This invention relates to battery holders and, more particularly, to a battery holder which allows a battery cell to be easily inserted into or removed from a housing while eliminating electric shock hazards to the user.
Many electronic systems which are powered from an external source also include an internal backup power source, typically one or more battery cells, to insure that internal memory settings are not erased in the event of failure of the external power source. One such type of electronic system is a telecommunications module used by small businesses to provide telephone service for the business at a particular location. Such a module includes an internal random access memory (RAM) for storing information unique to that business location such as, for example, telephone numbers for use in speed dialing. In the event of a total loss of power, the module would have to be reprogrammed.
In the past, many of these modules were provided with backup batteries that were permanently secured, as by soldering, to the printed wiring boards within the module enclosure. For servicing of these backup batteries, the printed wiring board would be removed from the enclosure and returned to the factory or service area, and a replacement board would be installed and programmed. Such servicing is therefore very time consuming and expensive. It would therefore be desirable to provide such an electronic system with backup batteries that are readily available from commercial sources and that are easily replaced by the user.
Since the purpose of providing backup batteries is to insure that the memory is not erased due to loss of power from the external source, changing of the batteries should be effected without the system being powered down. However, Underwriters Laboratory requires that there be no potential electric shock hazard to a user when replacing the batteries, as set forth in standard UL1950. Since an internal fault in the module could put a high voltage on the internal battery terminals, past practice required that the system be powered down in order to satisfy UL standards when replacing backup batteries. It would therefore be desirable to provide an arrangement whereby the backup batteries are readily separable from the internal battery terminals for replacement purposes and access to the internal battery terminals is severely restricted when the batteries are removed from the module so that the module can continue to be powered.